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Using an appropriate grouping of terms, a radiation force expression for cylinders in a standing wave based on far-field scattering [Wei et al., J. Acoust. Soc. Am.116, 202–208 (2004)] is transformed to an expression given elsewhere [F. G. Mitri, Eur. Phys. J. B44, 71–78 (2005)]. Mitri’s result is from a near-field derivation for the specific case of a circular cylinder. The far-field derivation also applies to noncircular objects having mirror symmetry about the incident wave vector. Some aspects of far-field derivations of optical and acoustical radiation forces are noted as are some implications for the radiation force on cylinders in travelling waves.

This paper presents the recursive algorithm of stiffness matrix method with improved efficiency for computing the total and surface stiffness matrices for a general multilayered anisotropic media. Based on the eigensolutions commonly available for analysis of such media, the recursive algorithm deals with eigen-submatrices directly and bypasses all intermediate layer stiffness submatrices. The improved algorithm obviates the need to compute certain inverse of the original scheme and makes the stiffness matrix recursion more robust. In situation where transfer matrix is numerically stable and easily accessible, an improved recursive algorithm is also given directly in terms of transfer submatrices without involving their explicit inverse.

A sperm whale (Physeter macrocephalus) was observed at the surface with above- and underwater video and synchronized underwater sound recordings. During seven instances the whale ventilated its lungs while clicking. From this observation it is inferred that click production is achieved by pressurizing air in the right nasal passage, pneumatically disconnected from the lungs and the left nasal passage, and that air flows anterior through the phonic lips into the distal air sac. The capability of breathing and clicking at the same time is unique among studied odontocetes and relates to the extreme asymmetry of the sperm whale sound-producing forehead.

The acoustical Wave Propagator (AWP) scheme involves an effective time-domain calculation of sound propagation using the combination of Chebyshev polynomial expansion and the Fourier pseudospectral method. The accuracy of this scheme degrades when the media has discontinuities due to the well-known Gibbs phenomenon. In this paper, several issues concerning AWP are addressed, including an analysis of the effect of Gibbs phenomenon on the accuracy. A mapped pseudospectral method is proposed wherein the grid points are redistributed, with the emphasis across the media discontinuities by a pre-determined smooth mapping curve, then the spatial derivatives are calculated through a modified Fourier pseudospectral method. Using this method, the influence of the Gibbs phenomenon is effectively alleviated while the computational efficiency of AWP is still maintained. The superiority of this improved AWP scheme is illustrated by three one-dimensional (1-D) numerical examples.

A stably stratified atmosphere supports propagation of internal gravity waves (IGW). These waves result in highly anisotropicfluctuations in temperature and wind velocity that are stretched in a horizontal direction. As a result, IGW can significantly affect propagation of sound waves in nighttime boundary layers and infrasound waves in the stratosphere. In this paper, a theory of sound propagation through, and scattering by, IGW is developed. First, 3D spectra of temperature and wind velocityfluctuations due to IGW, which were recently derived in the literature for the case of large wave numbers, are generalized to account for small wave numbers. The generalized 3D spectra are then used to calculate the sound scattering cross section in an atmosphere with IGW. The dependencies of the obtained scattering cross section on the sound frequency, scattering angle, and other parameters of the problem are qualitatively different from those for the case of sound scattering by isotropic turbulence with the von Kármán spectra of temperature and wind velocityfluctuations. Furthermore, the generalized 3D spectra are used to calculate the mean sound field and the transverse coherence function of a plane sound wave propagating through IGW. The results obtained also significantly differ from those for the case of sound propagation through isotropic turbulence.

We derive the Debye-series expansion of the normal transmitted plane wave through a water-saturated porous plate. By using relations from Biot’s theory, the theoreticaltransmission coefficient of the plate is related to a limited number of unknown parameters (velocity, attenuation coefficient of the fast and slow wave,reflection coefficients at the interfaces of the plate). They are determined via a comparison with the experimental transmission coefficient. The measurements show that the attenuation of the dilatational waves scales as the second power of frequency.

Approximate boundary conditions for an infinite elastic layer immersed in a fluid are derived. By using series expansions in the thickness coordinate of the plate fields, the displacements fields are eliminated, adopting the three-dimensional equations of motion. The sums and differences of the boundary pressure fields and their normal derivatives are related through a set of approximate boundary conditions, one symmetric and one antisymmetric. These equations involve powers in the layer thickness together with partial derivatives with respect to time as well as the spatial variables in the plate plane. The approximate boundary conditions can be truncated to an arbitrary order, and explicit relations are presented including terms of order five. Comparisons are made with effective boundary conditions using classical plate theories. The numerical examples involve reflection and transmission of plane waves incident on the plate at different angles, as well as the pressure fields due to a line force. Three fluid-loading cases are studied: modest, heavy, and light loadings. The results using truncated approximate boundary conditions are compared to exact and classical plate solutions. The examples show that the accuracies of the power series approximations of order three and higher are very good in the frequency interval considered.

A model consisting of uniformly distributed concentrated transient sources in closed reverberant systems is used to construct predictions for the diffuse field correlation function and its variance. Such correlations are useful for passive imaging. It is found that the variance is small compared with the square of the mean if estimates are based on a sufficient number of sources, and if a sufficiently long data record is taken from each source. Requirements are predicted to be most onerous at high frequency. Laboratory measurements support this theory. They furthermore indicate that the fidelity of the passively obtained correlation function to an actively obtained waveform depends, not only on having sufficient passive data, but also on an informed compensation for source spectrum and receiver characteristics. It is anticipated that these arguments will be relevant to convergence rates and fidelity for passive imaging in open systems such as are found in seismology and ocean acoustics.

Computation of acoustic radiation from a baffled circular piston continues be an active area of investigation, both as a canonical problem and because of numerous practical applications. For time-harmonic radiation, exact series expansions are an attractive approach because they do not require numerical integration or limiting approximations. Here, series expansions due to Hasegawa, Inoue, and Matsuzawa [J. Acoust. Soc. Am.74, 1044–1047 (1983); 75, 1048–1051 (1984)] are shown to reduce to simpler expressions suitable for numerical computations of piston fields in lossless and attenuative fluid media. For the region , where is the piston radius and is the distance from the piston center, an exact solution is given by an series of spherical Hankel functions and Legendre polynomials with explicit, closed-form, position-independent coefficients. For the paraxial region , where is the distance from the piston axis, a second exact series expansion is valid for all axial distances and reduces to the known analytic solution for . These two expansions allow the radiated field to be computed at any point, with rapid convergence except for points near the circle bounding the piston. Example numerical results illustrate application of this method to ultrasonic sources.

Detection of calcifications in breast is an important problem in the diagnosis of breast cancer. Vibro-acoustography is a recently developed method that uses the radiation force of ultrasound to create images of the mechanical response of an object at a low frequency using the magnitude or phase of the response. Small spheres are used to explore the use of the phase of vibration as a contrast modality for use in detection and identification of calcifications in breast tissue. An experiment is presented to measure the magnitude and phase of vibration at different frequencies. The theoretical and experimental results are compared for spheres of two different sizes. Phase images are shown in which five spheres of different density can be clearly distinguished from each other. With phase measurements and images, it is demonstrated that predictable imagecontrast exists for spheres of different density embedded in a viscoelastic medium.

In using the near-field acoustical holography based on the inverse boundary element method(BEM) for the reconstruction of vibroacoustic source parameters, an enormous number of measurements required in practice have limited the extended application of this method. To obtain the sufficient field data with a small number of actual measured data, the regeneration method of the radiated field using the multipoint equivalent sources is attempted in this paper. In using the equivalent source method, a vibrating source can be represented by distributed spherical sources inside the actual source surface. In this paper, the radiated field is expressed with a series of spherical Hankel functions and spherical harmonics. For suppressing the adverse effect of high-order spherical functions, spatial filtering of coefficients and wave-vector components by a regularization scheme is adopted. Restored field data appended with actual measured data can be used as input for the inverse BEM to reconstruct the source field. Numerical tests for spherical sources were performed for investigating the characteristics of the proposed technique. In order to validate the usefulness of the proposed method to actual irregular sources, a vacuum cleaner was taken as a demonstration example and good agreement between measured and reconstructed results could be observed.

For porous and granular materials, the dynamic characteristics of the solid component (frame) are important design factors that significantly affect the material’s acoustic properties. The primary goal of this study was to present an experimental method for measuring the vibration characteristics of this frame. The experimental setup was designed to induce controlled vibration of the solid component while minimizing the influence from coupling between vibrations of the fluid and the solid component. The Biot theory was used to verify this assumption, taking the two dilatational wave propagations and interactions into account. The experimental method was applied to measure the dynamic properties of glass spheres, lightweight microspheres, acoustic foams, and fiberglass. A continuous variation of the frame vibration characteristics with frequency similar to that of typical viscoelastic materials was measured. The vibration amplitude had minimal effects on the dynamic characteristics of the porous material compared to those of the granular material. For the granular material,materials comprised of larger particles and those under larger vibration amplitudes exhibited lower frame wave speeds and larger decay rates.

The effect of parametric wave phase conjugation (WPC) in application to ultrasound or acoustic waves in magnetostrictive solids has been addressed numerically by Ben Khelil et al. [J. Acoust. Soc. Am.109, 75–83 (Year: 2001)] using 1-D unsteady formulation. Here the numerical method presented by Voinovich et al. [Shock waves13(3), 221–230 (Year: 2003)] extends the analysis to the 2-D effects. The employed model describes universally elastic solids and liquids. A source term similar to Ben Khelil et al.’s accounts for the coupling between deformation and magnetostriction due to external periodic magnetic field. The compatibility between the isotropic constitutive law of the medium and the model of magnetostriction has been considered. Supplementary to the 1-D simulations, the present model involves longitudinal/transversal mode conversion at the sample boundaries and separate magnetic field coupling with dilatation and shear stress. The influence of those factors in a 2-D geometry on the potential output of a magneto-elastic wave phase conjugator is analyzed in this paper. The process under study includes propagation of a wave burst of a given frequency from a point source in a liquid into the active solid, amplification of the waves due to parametric resonance, and formation of time-reversed waves, their radiation into liquid, and focusing. The considered subject is particularly important for ultrasonic applications in acoustic imaging, nondestructive testing, or medical diagnostics and therapy.

We present a model applicable to ultrasound contrast agent bubbles that takes into account the physical properties of a lipidmonolayer coating on a gas microbubble. Three parameters describe the properties of the shell: a buckling radius, the compressibility of the shell, and a break-up shell tension. The model presents an original non-linear behavior at large amplitude oscillations, termed compression-only, induced by the buckling of the lipidmonolayer. This prediction is validated by experimental recordings with the high-speed camera Brandaris 128, operated at several millions of frames per second. The effect of aging, or the resultant of repeated acoustic pressure pulses on bubbles, is predicted by the model. It corrects a flaw in the shell elasticity term previously used in the dynamical equation for coated bubbles. The break-up is modeled by a critical shell tension above which gas is directly exposed to water.